The present invention relates to an apparatus for proportioning and mixing liquids and more particularly to such an apparatus for mixing liquids which while isolated are inactive and remain unchanged for protracted periods of storage and/or transportation even if subjected to adverse environmental factors, such as temperature, physical disturbance and the like, but which when mixed promptly become active or display marked changes in character, frequently with sudden effect.
For example, epoxy resins have become important factors in the plastic industry. They are recognized to have excellent chemical resistance, adhesion to glass and metals, electrical insulating properties, ease and precision of fabrication, and because of their small density change when they polymerize are popular for potting or encapsulating delicate electrical components. Their dimensional stability and durability have made them popular for dies used even for stamping metals. With proper fillers, they have tensile strengths approaching, and strength to weight ratios, exceeding those of steel. The epoxy resins are generally recognized as a most versatile class of cross linked polyethers.
In the preparation of epoxy resins, a low molecular weight diepoxy compound is first mixed with a cross-linking agent, plasticizers and such fillers as are desired to achieve desired characteristics. They are then permitted to cure at room temperature or with the application of heat.
In the making of epoxy resin products, intermediate diepoxy compounds are formed as the reaction products of epichlorohydrin and aliphatic or aromatic diols. The intermediate diepoxy compounds are quite stable, can be prepared to achieve a wide range of desired balance of properties but do not have useful physical properties in themselves until they are polymerized further. Such polymerization may be initiated by any suitable catalyst such as boron trifluoride, tertiary amines, organic acids, alchohols, merchaptans, primary and secondary amines, and polyamines.
However, as useful as epoxy resins are known to be, their production is subject to well known difficulties for which the industry has long sought dependable solutions. In many instances the proportions of the constituents making up the intermediate diepoxy compounds and the proportions of the intermediate diepoxy compounds and their catalysts must be more accurately controlled than can be readily accomplished in a dependable manner by previously known equipment. It is the usual practice to supply the intermediate diepoxy compounds by means of a metering pump and to supply the catalysts by means of a further metering pump. In many instances, the operation of such pumps cannot be sufficiently precisely controlled and the resultant mixture of diepoxy compounds and catalysts vary in proportion and characteristics. Further, in such systems it is possible for one pump to deliver while the other pump does not deliver at all or delivers in a restricted manner. Further, if a pump or its associated conduits, becomes clogged, the other pump and its conduits continue to produce without restriction. Further, conventionally it is the usual practice to intermingle the constituents of epoxy resin prior to their entering a mixer of some type. Such systems are notoriously difficult to clean and frequently become so clogged as to preclude further utilization.